1. Field of the Invention
The present invention relates to a method for fabricating triode field emitter array using carbon nanotubes having excellent electron emission characteristics.
2. Description of the Related Art
In a conventional field emission display (FED), when a strong electric field is applied through gates to a Spindt""s field emitter array (FEA), which is formed of a metal such molybdenum (Mo) or a semiconductor material such as silicon (Si), that is, to microtips arranged at regular intervals, electrons are emitted from the microtips. The emitted electrons are accelerated toward an anode, to which voltage (for example, several hundred to several thousand volts) is applied, and collide with phosphors with which the anodes are coated, thereby emitting light. Because the work function of a metal or a semiconductor material used for the microtips of a conventional FED is large, the gate voltage for electron emission must be very high. Residual gas particles in vacuum collide with electrons and are thus ionized. Because the microtips are bombarded with these gas ions, the microtips as an electron emission source may break. Moreover, since particles are separated from the phosphors colliding with electrons and pollute the microtips, the performance of the electron emission source may be deteriorated. These problems may reduce the performance and life time of the FEA. To overcome these problems, instead of a metal or a semiconductor material, carbon nanotubes having a low electron emission voltage and an excellent chemical stability is used for electron emitters. In this case, the performance and life time of the FEA can be improved.
Arc discharge and laser ablation is widely used in deposition of carbon nanotubes, but these methods are not suitable for mass production of carbon nanotubes at a low cost, and structure control is difficult in these methods. To overcome these problems, chemical vapor deposition has been developed. Representative chemical vapor deposition methods include thermal chemical vapor deposition (CVD) (Appl. Phys. Lett. 67, 2477, 1995) MPECVD (App. Phys. Lett. 72, 3437, 1998) and ion beam irradiation (Appl. Phys. Lett. 69, 4174, 1996).
While the threshold electrical field of a diamond film for electron emission, which has been highlighted as a material of an electron emission source, is about 10 V/xcexcm, carbon nanotubes have a characteristic in which electrons are easily emitted even at an electrical field of 1 V/xcexcm or less. Accordingly, carbon nanotubes have been touted as the next generation material of an electron emission source.
FIG. 1 is a schematic sectional view illustrating the structure of a conventional FED using carbon nanotubes. As shown in FIG. 1, the conventional FED using carbon nanotubes includes a front substrate 11 and a rear substrate 16 which face each other, an anode electrode 12 and a cathode electrode 15 which are formed on the surfaces of the two substrates 11 and 16 facing each other, respectively, phosphor 13 with which the anode electrode 12 is coated and carbon nanotubes 14 deposited on the cathode electrode 15, thereby having a diode structure.
It is crucial to deposit carbon nanotubes on a wide area at a low cost using a method capable of controlling the carbon nanotubes in manufacturing FEDs using carbon nanotubes. It is considered that chemical vapor deposition should be used to achieve the above purpose. Similarly to arc discharge or laser ablation, chemical vapor deposition uses a transition metal such as nickel (Ni) or iron (Fe) or silicide such as CoSi2 as a catalyzer. Up to now, carbon nanotubes are not deposited on a structure of a predetermined pattern but have still been deposited randomly as in a diode structure. The diode structure can easily be manufactured by chemical vapor deposition because a layer such as an insulating layer or a gate shown in a triode structure is not necessary. However, it is difficult to control emitted electrons in a simple diode structure. This disturbs the required performance of a display.
A field emitter using controlled carbon nanotubes is disclosed in U.S. Pat. No. 5,773,834. In this patent, a field emitter is formed in a triode structure using a grid of a net shape as gate electrodes so that it can be expected that emitted electrons can be controlled to some extent. However, the structure of this field emitter is not simple enough to be easily manufactured by chemical vapor deposition.
To solve the above problem, an object of the present invention is to provide a method for fabricating a triode-structure carbon nanotube field emitter array, in which an electron emission source is fabricated by applying a Spindt process to carbon nanotubes.
To achieve the above object, in one embodiment, the present invention provides a method for fabricating a triode-structure carbon nanotube field emitter array. The method includes the steps of (a) forming a separation layer on a gate electrode using slant deposition in a structure in which a cathode electrode, a gate insulation layer and the gate electrode are sequentially formed on a cathode glass substrate, a gate opening is formed on the gate electrode, a micro-cavity corresponding to the opening is formed in the gate insulation layer; (b) forming a catalyst layer on the cathode electrode within the micro-cavity, the catalyst layer acting as a catalyst in growing carbon nanotubes; (c) performing slant deposition on the catalyst layer, thereby forming a non-reactive layer for preventing carbon nanotubes from growing on the catalyst layer outside the micro-cavity; (d) growing carbon nanotubes on the catalyst layer within the micro-cavity; and (e) removing the separation layer.
In the step (a), the gate insulation layer is formed by depositing SiO2 or Si3N4 to a thickness of 5-10 xcexcm, and the diameter of the gate opening is 5-10 xcexcm. In the step (b), the catalyst layer is formed by depositing Ni or Co. In the step (c), the non-reactive layer is formed of at least one material selected from among Cr, W, Al, Mo and Si. In the step (d), the carbon nanotubes are grown by an arc discharge method or chemical vapor deposition methods.
In another embodiment, the present invention provides a method for fabricating a triode-structure carbon nanotube field emitter array. The method includes the steps of (a) forming a separation layer on a gate electrode using slant deposition in a structure in which a cathode electrode, a gate insulation layer and the gate electrode are sequentially formed on a cathode glass substrate, a gate opening is formed on the gate electrode, a micro-cavity corresponding to the gate opening is formed in the gate insulation layer; (b) performing slant deposition of the cathode electrode within the micro-cavity, thereby forming a base layer having a truncated cone shape within the micro-cavity; (c) forming a catalyst layer on the base layer, the catalyst layer acting as a catalyst in growing carbon nanotubes; (d) performing slant deposition on the catalyst layer, thereby forming a non-reactive layer for preventing carbon nanotubes from growing on the catalyst layer outside the micro-cavity; (e) growing carbon nanotubes on the catalyst layer within the micro-cavity; and (f) removing the separation layer.
In the step (a), the gate insulation layer is formed by depositing SiO2 or Si3N4 to a thickness of 5-10 xcexcm, and the diameter of the gate opening is 5-10 xcexcm. In the step (b), the base layer is formed of at least one material selected from among Au, Pt and Nb. In the step (c), the catalyst layer is formed by depositing Ni or Co. In the step (d), the non-reactive layer is formed of at least one material selected from among Cr, W, Al, Mo and Si. In the step (e), the carbon nanotubes are grown by an arc discharge method or chemical vapor deposition methods.